This study is concerned with the problem of a pipe containing a part-through or a through circumferential crack. First@ the stress intensity factors for an internal or an external circumferential surface crack in a pipe are obtained. The main objective here is to give the necessary theoretical information for the treatment of subcritical crack growth process. Next the problem of a through crack in the presence of large scale plastic deformations is considered. The crack opening displacement (COD) is used as the main parameter to analyze the fracture instability problem and to correlate the experimental results. In the analytical part of the study Reissner's shell theory and an elastic or elastic-plastic line spring model are used to formulate the problem. The experiments were performed on 20-inch diameter X60 line pipes. A 0.025-inch wide starter notch was introduced to the pipes which were then subjected to cyclic loading under four point bending. The limited data obtained from the fatigue tests give the expected result@ namely that the crack propagation rate in pipes may be predicted from the baseline data obtained from simple specimens provided the stress intensity factors for pipes are calculated with sufficient accuracy. The ductile fracture results show that the technique based on the asymptotic behavior of COD may be quite useful in determining a conservative estimate of the fracture instability load.